If the division of the spoils at Sunday's Oscar ceremony was intended as an exercise in diplomacy, then its execution was almost flawless.

No film dominated the proceedings and while many of the front-runners emerged triumphant, there were also enough surprises to ensure that the key categories embraced the widest range of contenders. Six films shared the top six Oscars.

The biggest upset came when Crash, the ensemble race relations drama set in Los Angeles, swiped best picture Oscar from the clear favourite Brokeback Mountain, the cowboy-themed gay love story starring Heath Ledger and Jake Gyllenhaal.

The defeat of Brokeback Mountain was described as one of the most unexpected twists in the history of the awards, which seldom deviate much from the expected script.

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It was a good night for British talent, with Rachel Weisz winning best supporting actress for her role in The Constant Gardener and awards veterans Nick Park and Steve Box picking up their first animated feature film Oscar for Wallace & Gromit: The Curse of the Were-Rabbit.

The mischievous and often outlandish London playwright Martin McDonagh, who once became so drunk at an awards ceremony that he picked a fight with Sean Connery, won the Oscar for best short film for Six Shooter, his first big screen foray.

Best actress nominees Keira Knightley and Dame Judi Dench were, however, beaten by Reese Witherspoon, who won for her performance as the country singer June Carter in Walk the Line, the Johnny Cash biopic.

Capping an almost unbroken run of award season wins, Philip Seymour Hoffman was named best actor for his portrayal of the homosexual writer Truman Capote in Capote. George Clooney won the best supporting actor award for Syriana.

Despite the fact that the Academy's top honour has never been given to a film with explicit homosexual themes, many had cast Brokeback Mountain as this year's Million Dollar Baby, the Clint Eastwood film that earned last year's best director and picture Oscars.

It was short-listed in a leading eight categories and ended up with three, including a best director Oscar for Ang Lee, who became the first Asian film-maker to win Hollywood's top film-making prize.

Crash also won three awards, including best film editing and best original screenplay for its Canadian director Paul Haggis, who also wrote Million Dollar Baby.

He dedicated the award to "the people out there who stand up for peace, and justice, and against intolerance" and commented "this was a year when Hollywood rewarded rule-breakers".

Much was made of the political focus of many of the short-listed films, which tended to be smaller, independent productions rather than big budget epics such as previous winners Titanic and Lord of the Rings. Some interpreted the selection as the Academy snubbing Middle America to indulge its desire to reward well-intentioned niche endeavours.

Others saw it more as a reflection of the times - when box office revenues are sinking and low-budget offerings from outside Hollywood can trump costly studio fare.

Crash was a particularly unusual winner as it was filmed outside the system for just £3.7 million, despite a high-profile cast including Matt Dillon, Don Cheadle and Sandra Bullock, before being picked up by Lionsgate, the independent distributor.

The film became a hit, grossing £31 million in the US.

Accepting the best picture Oscar, Cathy Schulman, the producer, said: "You have made this year one of the most breathtaking and stunning maverick years in American cinema."

Rachel Weisz, who turns 35 today, said she had been so overwhelmed by her win she was momentarily distracted from her baby's kicking. The actress, almost seven months pregnant with her first child, looked dazed as she came off stage, remarking: "I'm so tripped out right now. I'm sorry, I'm not normal."

Weisz, who also won the Golden Globe and the Screen Actors Guild for her role as a fearless humanitarian-aid worker in the corporate thriller, adapted from a John le Carré novel, said pregnancy had made her brain "like porridge".

However, she was enjoying being "a part of a moment where fiction is holding a mirror up to contemporary culture and asking questions about what's going on".

McDonagh's win was one of the more surprising of the evening, given that Six Shooter was his first attempt at writing or directing a film.

McDonagh, 35, has always been a bit of a character, having been born in London to Irish parents, a construction worker and a dinner lady. Six Shooter, a black comedy about a man who meets a strange and possibly dangerous youth on a train on the day his wife has died, was made in Ireland for just £80,000.

Oscar night passed without any of the emotional outbursts that have been a feature of previous years.